I was quite disappointed that we didn't get to see Iron Man fight Ben Kingsley's Mandarin, especially as the trailers really hyped the Mandarin up and I'd been waiting to see it since the first film. I thought the twist was hilarious, but seemed a bit insulting to what I've always viewed as Iron man's arch-enemy, especially as all of his attributes were transplanted into Killian (who I honestly expected to turn into Fing-Fang-Foom at the end, he got so intense and over-the-top).
I liked the film and what they did, but felt I would've been just as happy, if not more so, if the Mandarin had been the Mandarin and had been manipulating Killian, rather than the other way around (but I guess that manipulating corporate-types is a bit of a cliche these days). I dunno; I loved watching the Iron Man animated series, where Iron Man/Mandarin fights were a big thing, and I felt like Iron Man Three (what was up with spelling the 3 out anyway?) missed out a bit there.